Students present all sorts of interesting learning problems.
I have two students who studied for nearly the same amount of years. One student practiced the entire form whereas one practiced just the first section.
For beginners it is always better to focus on just the first section for at least 6-12 months if only to get the foundation work in. After that its good to learn the whole form to build a database of movements.
However, if a student were to keep learning the same first section for a few years he can also be very good, perhaps even better than the student who did the entire form.
The funny thing is that this did not pan out and the student who did the entire form for a few years actually turned out to have a better body feel. So why did it turn out this way?
Perhaps its a matter of the person learning. Perhaps its other factors.
Anyway, the student who did the entire form seems to have a better adhere and don’t react wildly reaction when attacked whereas the student who did only the first section has hands that are better for attacking but not so much for defending because the same reaction that is good for attacking is also bad for playing the lay-prey-n-trap game that we sometimes do in push hands. By moving too much he creates too many openings and opportunities for an astute opponent to take advantage of.
Conclusion – sometimes learning too much is no good, but in some cases good. The same can be said for learning too little. The middle ground could perhaps be the best.